Paper tools, including paper punches, staplers, and paper trimmers, are configured such that force input by a user results in an operation on paper or other substrates. For example, in a typical paper punch, the user actuates a handle, which causes a punch pin to move downwardly to punch a hole in a stack of sheets inserted into the punch. Punches that employ a linkage to actuate the punch typically include links generally aligned above a vertically oriented punch mechanism. The linkage increases the mechanical advantage within the punch such that less force input is required from the user to perform the punching operations. Staplers are also known that include linkages for increasing the mechanical advantage of the stapler during stapling operations. Paper trimmers can also be configured to contain similar linkages for increasing mechanical advantage.
Four-bar linkages are known in the construction of paper punches and staplers. One example of such a four-bar linkage in a paper punch is shown in U.S. Pat. No. 6,688,199 and prior-art FIG. 1. FIG. 1 illustrates a paper punch 100 generally including a base 110, punch pins 112 (only one shown), and a linkage for actuating the punch pins 112. The linkage is configured as a four-bar linkage including a drive member 114, a first end cap 118, and a handle member 122. The drive member 114 is pivotably coupled to the base 110 at pivot 120, and the handle member 122 is pivotably coupled to the drive member 114 at pivot 126. The handle member 122 is also pivotably coupled to a second end cap (not shown—positioned at one end of the punch 100) at pivot 134, while the second end cap is pivotably coupled to the base 110 at pivot 138.
FIG. 1 also schematically illustrates the “links” representative of the base 110, drive member 114, handle member 122, and the second end cap in a four-bar linkage. The base 110 is schematically illustrated by link 142, which is representative of the “ground,” which is stationary in a four-bar linkage. The second end cap is schematically illustrated by link 146, which is representative of the “crank” in a four-bar linkage. The drive member 114 is schematically illustrated by link 150, which is representative of the “rocker” or “output link,” which provides the output force or motion to the pivot pins 112. The handle member 122 is schematically illustrated by link 154, which is representative of the “coupler” or “coupler link,” which connects the link 146 (the “crank”) and the link 150 (the “rocker”) in the four-bar linkage.
Such a four-bar linkage, when utilized in a paper punch, includes three movable links (i.e., the links 146, 150, 154) and a sliding point of contact, whether rotationally sliding or through an elongated cam slot. In the paper punch 100 illustrated in FIG. 1, a push bar in the form of a cylindrical rod 158 is received in respective grooves 162 in the drive members 114. During actuation of the punch pins 112, sliding contact occurs between the rod 158 coupled with the drive members 114 and the punch pins 112 to transfer the pivoting motion of the drive members 114 to linear motion of the punch pins 112.
In typical manually-operated staplers, the upper cover often directly applies a force to the staple driver to drive a staple into a stack of sheets or other materials. Other staplers, such as the staplers shown in U.S. Pat. Nos. 6,966,479, 6,550,661, 6,776,321, and 6,179,193, have used the leverage provided by two pivots and a sliding contact, rather than a four-bar linkage. Such staplers have only a main body pivot and a cover or handle pivot. The pivot between the magazine and the cover can facilitate opening the stapler for staple loading. Cam slots have been used in staplers, such as the stapler shown in U.S. Pat. No. 6,966,479, but only to provide clearance for opening the upper cover when loading staples into the stapler magazine. Such cam slots have not been used in the mechanism or linkage that transmits power to the staple driver.